Menstrual cycles have several days at the beginning that are infertile (pre-ovulatory infertility), a period of fertility, and then several days just before the next menstruation that are infertile (post-ovulatory infertility). The first day of bleeding is considered day one of the menstrual cycle.
How to find out Longest and shortest period cycle?
You have to note your period for at least 6 months and note the number of days between starting date and the next period. Then identify longest and shortest period cycles.
Calculation of Safe Period
The calendar method is most reliable if a woman has a regular period cycle. It is also based on the assumption that ovulation in most ladies takes place at about fourteenth day before the next menstrual flow. The implication of the above is that in a regular period cycle, it can be assumed that ovulation will take place on the fourteenth day before the next period.
If for example, a women’s menstrual cycle varies from 26 days to 31 days cycle.
The shortest cycle [26days] minus 18days = 8th day.
The longest cycle [31days] minus 10days = 21st day.
8th to 21st day of each cycle counting from first day of menstrual period is considered as fertile period. Period other than this fertile period in a menstrual cycle is considered as safe period.
The major shortcoming is that the calendar method could be quite tricky, since the pattern of fertility can suddenly change appreciably in the same person over time. Like some ladies would have realized that sometime ago their cycles might have hovered around 28 days and later came down to say 24 days or more – that is stretching to say 33 days. This is common and may be normal.
Safe period is not 100% reliable and so caution should be taken.
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